feat(core): persist v2 session context epochs (#30789)

packages/core/src/database/migration/20260605003541_add_session_context_snapshot.ts

@@ -0,0 +1,21 @@
+import { Effect } from "effect"
+import type { DatabaseMigration } from "../migration"
+
+export default {
+  id: "20260605003541_add_session_context_snapshot",
+  up(tx) {
+    return Effect.gen(function* () {
+      yield* tx.run(`
+        CREATE TABLE \`session_context_epoch\` (
+          \`session_id\` text PRIMARY KEY,
+          \`baseline\` text NOT NULL,
+          \`snapshot\` text NOT NULL,
+          \`baseline_seq\` integer NOT NULL,
+          \`replacement_seq\` integer,
+          \`revision\` integer DEFAULT 0 NOT NULL,
+          CONSTRAINT \`fk_session_context_epoch_session_id_session_id_fk\` FOREIGN KEY (\`session_id\`) REFERENCES \`session\`(\`id\`) ON DELETE CASCADE
+        );
+      `)
+    })
+  },
+} satisfies DatabaseMigration.Migration